Okay, i picked a top day here to try this (its 33 deg here... ) cooling water going in (after cruising through my 18M of black hose sitting partially in the sun) was 25deg,
at a wort flow of 1.2Lpm and water flow of 5lpm wort output was 35 deg
at .6lpm and 3.5lpm it was 29
at .6lpm and 1.2 lpm my thermometer gave up...i would guess it was slightly warmer than the 29... but less than 35..
in winter, this is going to kick arse... in summer though i think im going to need a secondary chiller (i think it will be a copper coil in a bucket of ice...)